Distribution Overhead Line Monitoring with LEM’s ART Rogowski coil
New line current sensors allow utilities to monitor their overhead distribution lines to maximize theircapacity and prevent clearance violations thus improving reliability and efficiency of the MV
Distribution Grid.
The High Voltage transmission grid is already highly automated and monitored through SCADA andEnergy Management Systems. In contrast, the Medium-Low Voltage distribution grid has very limited
monitoring and control. Why? - More often than not, Utilities fail to monitor their many medium voltage
substations, this is due to the expense of retrofitting with today’s solutions and of the time it takes toplan and build. The implementation of traditional substation monitoring requires complicatedengineering, this includes the use of remote terminal units with new conduits, wiring to relays andcurrent transformers. Engineers must schedule outages to disconnect the feeders, which takes timeand may only be possible during low power consumption needs. Once the hardware has been installed,
the utility has to program and integrate all the hardware into a complex SCADA system, which is asignificant and difficult challenge for many utilities. There must be a better way.
Below the feeder level, remote monitoring is absent with the exception of customer billing meter points
where smart meters are becoming prevalent to read, monitor and control. However, these smart meters
are only collecting and communicating Voltage, Current , Power, Reactive Power, S, Energy data rather
than power quality data sets like Cos (Phi), Total Harmonic Distortion, flicker, voltage dips, transients,waveforms, time series etc. The smart meter does not collect a lot of data outside of its billing focusedfunction. Substations and distribution power lines are two of the most valuable assets for utilities that
require crucial power flow data to provide the most reliable service.
The most relevant data in the distribution grid is about the location and cause of faults and non-fault
events, high-impedance faults, consumption peaks, handling distributed renewable energy and EV
charging, feeder outages, and many others – all high-value data that is not addressed by today’ssystems.
Now monitoring overhead power lines has been made possible faster, easier and cheaper with newInternet of Things telecom networks like NB-IoT and LPWAN.Thanks to a line sensor (1), installed
between two MV poles (2), the grid operator can visualize, in real-time, the current flow in order tooptimize the power line capacity to distribute more electricity. The wireless line sensor (1) sends dataover a telecom relay (3) to a secured database in the cloud (4) or on premise. The energy management
platform (5) can regulate, alert and notify the maintenance team if needed. New line sensors are now
using the LEM Rogowski coil ART (A) to measure the current, detect line aging depending on the levelof current, and prioritize line capacity.

A.
1.
2.
3.
4.
5.

LEM ART
Line Sensor
MV Power Lines
Telecom relay
Cloud and database
Energy Management

1ABefore without visibility about the grid, the generated renewable energy distributed through an overheadline could be overloaded (red). Thanks to the three-phase line sensor system, the extra power in oneof the line can be re-distributed to the adjacent lines (black) therefore reducing the initial line (blue)
capacity to an acceptable level. Overall, the capacity output of the power grid is then maximized (fig.
1).

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Figure 1: Before and after line sensor installation
In addition, the line sensor (1-35kV distribution grid) provides periodic time synchronized measurements
to facilitate improved situational awareness and operations: current, both amplitude and phase,
conductor surface temperature and detects fault conditions enabling rapid identification and notification.
This three phase line sensor system in the power distribution are equalized in real-time among thedifferent lines within a meshed network
The AC measurement can now be achieved with the LEM ART split-core rogowski coil, see below table
for the summary of the ART advantages compared to two other current measurement techniques usedin the Line sensor.

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Transformer inside

Resistor inside

Current sensor
technology

Split-core current
transformer

Split-core Rogowski coil

LEM ART split-core
Rogowski coil

Current range

Many versions: 80A,100A, 300A, 400A,600A, 800A…

One version fits all

One version fits all

Electromagnetic
compatibility

N/AYes (Resistor)

N/A (Ferrite inside)

Accuracy0.5%

1%

0.5%

WeightHeavy

Light

Lightest (~100g)

Safe output ofcurrent sensor

Precaution (currentoutput)

Safe

Safe (di/dt output)

Protectionrating

IP 65 with protectivehousing

IP 64

IP 57

-40 to +80C

-40 to +70C

-40 to +80C

$$$

$$

$

Operatingtemperature
PRICE

Ferrite inside

ART is the clear winner of this comparison with a practical one size fits all current loop, excellent ferritecore, great accuracy, light, safe mV output and water resistant coil
ART Ferrite core
Recent developments have revolutionized the characteristics of ferrite at 50/60Hz, bringing many
advantages. This new type of ferrite has significantly improved permeability and has been implemented
in this ART Rogowski coil (fig. 2). ART takes advantage of the intrinsic ferrite qualities:
High accuracy and excellent linearity, even at very low current levels
No phase-shift between input and output currents
No air gaps and virtually insensitive to ageing and temperature changes
Low position dependent error close to the clasp of the coil (see ART Sensitivity)
Low cost versus potentiometer based Rogowski coils

Figure 2: Ferrite core of LEM ART Rogowski coils

4ART Sensitivity
The overall sensitivity to the position of the primary conductor can be controlled, but usuallyclose to the clasp errors are often unavoidable, except for the patented ferrite based ART
Rogowski coil (fig. 3).

Figure 3: Position sensitivity of ART Rogowski coilConclusion
The new ART Rogowski coil class 0.5 has made huge progress, allowing small, light, sensitive andflexible current sensing for MV grids. The major improvements that have been made in the design andmanufacturing processes have enabled a reduction in both the cost and the sensitivity to the coilpositioning around the primary cable.
People consume more electricity than ever before and have an expectation that they will access theirelectricity without fault or interruption. The line sensor provides situational awareness along distribution
feeders allowing utilities to operate and respond based on prevailing conditions. The system directs
preemptive patrol and maintenance crews to the affected grid locations, enabling utilities to avoid
potential short or long electricity interruptions. It reduces outage frequency, resulting in the reduction of
the momentary average interruption frequency index (MAIFI) and system average interruption
frequency index (SAIFI). Both indexes serve as valuable tools for evaluating a utility’s performance andreliability because some countries have already put in place regulations that require a utility to reimburse
customers for long electricity interruptions.
When installed with the hot stick or insulated gloves on the overhead power line, LEM ART rogowski isa safe, easy-to-install, light but robust current measurement alternative to heavy and expensive current
transformers, therefore improving the overall performance, reliability and efficiency of the line sensor.
About LEM
LEM is the market leader in providing innovative and high-quality solutions for measuring electricalparameters for a broad range of applications. LEM answers the demand for an accurate, reliable andeasy-to-install energy sensor for future Smart Cities.

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